Honestly, I remember being quite blur about this when my gynae mentioned it during my detailed scan too. From what I know, the normal range can vary and your gynae is really the best person to explain what your specific reading means for your stage of pregnancy. I would not stress too much over the numbers you read online because every pregnancy is different, and what matters is what your own doctor says in context. Do bring it up at your next appointment and ask them to walk you through the results, so you have a clear picture rather than worrying on your own.